quarks exchanging gluons

[Aki]

Quarks emit gluons to change their "colour". This process happens a billions times each second within a single proton/neutron. What is the purpose of this process? What would happen to the proton/neutron if this process does not occur?

[Tormod]

The gluons are what binds the quarks together. Without the gluons the quarks would not stay together within the protons and neutrons.

[Aki]

But why do the quarks constantly need to exchange gluons? Can't they have the gluons stay where they are?

[Tormod]

The exchange of gluons is how the particles interact. Gluons do not exist "freely" but only as transmitters of the strong force within the atomic nucleus. So the constant exchange is necessary, or else the particles would not have any way to interact.

If you see the particles as a sort of radiation being emitted and absorbed it makes more sense.

[lindagarrette]

So, what causes gluon emmission in the first place? I.e., what is the force or interaction that initiates a quark color change? I sort of understand this explanation below from "The Particle Adventure" website but would like to know why?



Color charge is always conserved.

When a quark emits or absorbs a gluon, that quark's color must change in order to conserve color charge. For example, suppose a red quark changes into a blue quark and emits a red/antiblue gluon (the image below illustrates antiblue as yellow). The net color is still red. This is because - after the emission of the gluon - the blue color of the quark cancels with the antiblue color of the gluon. The remaining color then is the red color of the gluon.

Quarks emit and absorb gluons very frequently within a hadron, so there is no way to observe the color of an individual quark. Within a hadron, though, the color of the two quarks exchanging a gluon will change in a way that keeps the bound system in a color-neutral state.

[BlameTheEx]

Anybody ever seen a quark, or a gluon for that matter? How about observation of colours?

Like Dark Energy, I wonder if we are doing more than giving names to our ignorance.

[Tormod]

Originally Posted by BlameTheEx

Anybody ever seen a quark, or a gluon for that matter? How about observation of colours?

Like Dark Energy, I wonder if we are doing more than giving names to our ignorance.

Ever the naysayer, aye?

Particle physics (and indeed quantum mechanics) may well turn out to be hogwash one day but gluons are real currency as far as physics are concerned.

Here's what Wiki says about them:
http://en.wikipedia.org/wiki/Gluons

By the way, has anyone seen an intention? Hm...then they probably do not exist, and are but figments of our ignorance.

[Aki]

Ah I get it now.

About what Blame said: I think I read somewhere that they have seen quarks and gluons, and both of them are always seen together. So they have not seen a quark without a gluon and vice versa. As to the colour thing, the quarks do not have a "visual colour". The "colour" is used to describe their "state"

[maddog]

As Blame was jesting. There has not been any visual evidence of gluons or quarks
directly as no free quarks have ever been found. However, QCD is very accurate at
predicting the parameters in the resonances for all the particles found by colliding with
each other to high accuracy. This in essence is the Standard Model so far.

String Theory early on was considering that for open strings the ends were the quarks.
This is still being debated today even with M-Theory as far as I can tell.

Maddog

[Bo]

for the original message: If the quarks don't exchange gluons, no force is emitted, and thus the proton would fall apart.

Anybody ever seen a quark, or a gluon for that matter? How about observation of colours?

No, because of asymptotic freedom (this years nobel prize), individual quarks cannot be seen. And since gluons couple only to quarks, these also cannot be seen directly. However the basis of the quark model has a firm experimental basis:

the fact that a proton has some internal structure, is a direct observational fact (see e.g. http://nobelprize.org/physics/educational/matter/15.html for the difference in scattering with and without internal structure)
Via all kind of measurements, the properties of the internal particles where fixed, including the fractional charge (1/3, 2/3); and the fact that there are 3 inside a proton (and other so-called 'hadrons') and 2 in a group of particles called mesons. However still some things where present that could't be understood. The need was then for an extra property (known as color). With the inlusion of color the quark model was completely described by 1 symmetrygroup. This meant that the force carriers of the quarks should also belong to this group. These particles are the gluons. Later things like gluon jets ( a gluon leaving the original particle, and immediatly decaying in a large bunch of other particles)where seen as observational proof of the model.